Computer systems typically contain one or more integrated circuits (ICs). High-speed ICs that consume a lot of power (on the order of a few Watts or more), such as, for example, processors and controllers, require that the heat generated by the IC be conducted away from the IC and dissipated. If the heat generated by the IC is not removed, performance of the IC is degraded. In some cases, an IC can become so hot that it will actually destroy itself, causing the computer system to stop functioning. Therefore, it is necessary to design heat removal systems into computer systems that use high power ICs such as processors.
A heat removal system typically comprises two main parts, a thermal block and a heat sink. A thermal block is the portion of the heat removal system that conducts heat from the IC and transfers the heat to the heat sink. A thermal block is typically highly thermally conductive, comprising a large, solid mass of metal such as copper or aluminum, for efficient transfer of the heat from the IC to the heat sink.
A heat sink is the portion of the heat removal system that dissipates the heat conducted from the IC (via the thermal block) to the ambient environment. A heat sink dissipates heat by either increasing the surface area for the heat to dissipate from, increasing air flow (or liquid flow) across a heated surface, or both. Some heat sinks include fins and heat spreader plates that increase heat dissipation surface area. Other heat sinks use a fan to blow air across a surface.
Some ICs are sold to computer system manufacturers prepackaged under thin metal lids that provide physical protection for the IC and shield the IC from electromagnetic interference. The IC typically arrives already thermally coupled to the metal lid, and the system manufacturer is responsible for then thermally coupling the metal lid to a thermal block, which is thermally coupled to a heat sink inside the computer system. Because the metal lid represents an intermediate thermal coupling between the IC and the thermal block, the thermal resistivity contributed by the thin metal lid degrades the overall efficiency of the heat removal system. This represents a reliability concern. In addition, for mobile computer systems, such as laptop, notebook, sub-notebook, and personal data assistants, space and weight constraints can severely limit the use of bulky, heavy thermal blocks.